Characteristic of entire corneal topography and tomography for the detection of sub-clinical keratoconus with Zernike polynomials using Pentacam

Zhe Xu,Yuanyuan Wang,Meixiao Shen,Mei Peng,Jianhua Wang,Xiran Zhuang,Jun Jiang,Wei Chen,Weibo Li,Fan Lu

doi:10.1038/s41598-017-16568-y

Abstract

The study aimed to characterize the entire corneal topography and tomography for the detection of sub-clinical keratoconus (KC) with a Zernike application method. Normal subjects (n = 147; 147 eyes), sub-clinical KC patients (n = 77; 77 eyes), and KC patients (n = 139; 139 eyes) were imaged with the Pentacam HR system. The entire corneal data of pachymetry and elevation of both the anterior and posterior surfaces were exported from the Pentacam HR software. Zernike polynomials fitting was used to quantify the 3D distribution of the corneal thickness and surface elevation. The root mean square (RMS) values for each order and the total high-order irregularity were calculated. Multimeric discriminant functions combined with individual indices were built using linear step discriminant analysis. Receiver operating characteristic curves determined the diagnostic accuracy (area under the curve, AUC). The 3rd-order RMS of the posterior surface (AUC: 0.928) obtained the highest discriminating capability in sub-clinical KC eyes. The multimeric function, which consisted of the Zernike fitting indices of corneal posterior elevation, showed the highest discriminant ability (AUC: 0.951). Indices generated from the elevation of posterior surface and thickness measurements over the entire cornea using the Zernike method based on the Pentacam HR system were able to identify very early KC.

Highlights

Iatrogenic keratectasia is the most feared complication after corneal refractive surgery[1,2]
The consensus standardized the definition of corneal ectasia procession, which included at least two of the following parameters: steepening of the anterior corneal surface, steepening of the posterior corneal surface, and progressive thinning and/or an increase in the rate of corneal thickness change from the periphery to the thinnest point[25]
This is the first study to comprehensively describe the properties of the entire 3D corneal topography and tomography in sub-clinical KC eyes using the Zernike polynomials modeling method

Summary

Introduction

Iatrogenic keratectasia is the most feared complication after corneal refractive surgery[1,2]. It is still a challenge to precisely distinguish a preclinical KC cornea from a normal cornea before refractive surgery, due to the lack of early-stage symptoms[7] Those with suspected bilateral KC often do not present typical signs and symptoms until a definitive KC develops in one eye[8]. Evaluating and characterizing the topography and tomography features of the corneas in these particular eyes may help clinicians to improve screening methods in order to distinguish suspected KC cases from normal corneas and prevent iatrogenic keratectasia after refractive surgery. The goal of the present study was to apply the Zernike fitting method to describe the 3D varying complexity of corneal shapes and the 3D distribution of corneal thickness, and to characterize the entire corneal topography and tomography data in sub-clinical eyes, KC eyes, and normal eyes using Pentacam tomography. The metrics constructed from Zernike polynomials were compared to improve the diagnostic sensitivity and specificity for the detection of sub-clinical KC corneas

Objectives

Methods

Results

Conclusion